1. Field of the Invention
This invention relates to a safety disconnect switch for serving as an anchor means of suspended electrical cables which will first disconnect the cable and then drop it harmlessly to the ground whenever an excessive tension force is exerted on the cable by a falling tree or the like.
2. Description of the Prior Art
Safety release mechanisms are widely used with overhead powerlines as is shown in the Rasmussen et al U.S. Pat. No. 3,519,727. In this patent, each safety release mechanism supports a single overhead powerline under normal conditions, and releases the line under abnormal longitudinal loads which might otherwise cause damage to the suspension towers. The release mechanism comprises a slide and a slide support. The slide support is pivotally attached to the suspension tower and the slide is pivotally attached to a transmission line. The slide is held against vertical and transverse forces by the support, and against longitudinal by a shear pin connecting the slide to the slide support so that when excessive longitudinal forces occur, the shear pin will break and the slide will become disengaged from the slide thereby disengaging the transmission line from the tower. When the transmission line is separated from the suspension tower, the line remains intact and continues to carry electrical current.
Another patent of this sort is the Grannis Pat. No. 3,711,049 which describes a mechanical load limiter for overhead powerlines for releasing a powerline from its suspension tower whenever an excessive mechanical load is put on a powerline so as to protect the tower from damage or destruction. This Grannis load limiter is fixed at one end to a powerline suspension tower, or pole arm, and at the other to an insulator attached to a powerline. Movement of the line beyond a predetermined limit in either direction causes the limiter to release the insulator, thereby dropping the single line and preventing damage to the tower.
A safety breakaway connector for use with multi-conductor service entrance cable is shown in the Bomgaars et al U.S. Pat. No. 3,761,865. This breakaway connector is attached to a utility pole to release the service entrance cable upon excessive pull on the cable, caused by falling limbs, high wind, ice accumulation, accident or the like. A push-pull disconnect is provided in each conductor of the service entrance cable adjacent the pole so that the wires will be disconnected automatically when the cable is released. The breakaway connector includes a pivotal detent bar which is longitudinally shiftable toward the cable against the bias of a heavy compression spring. The service entrance cable is connected to the detent bar by a ring looped around the bar. Cable tension on the ring tends to both rotate and longitudinally shift the bar. Under normal cable load conditions, the bar engages stop means to prevent its rotation. Excessive pull on the cable longitudinally shifts the bar away from the stop means to allow its rotation, which in turn releases the ring and cable from the detent bar.